Replacing tags inside the parent tag using DOM PHP

Here is what I got:

<div id="list">
<ol>
  <li>Ordered list 1</li>
  <li>Ordered list 2</li>
  <ul><li>Unordered list inside ol ul</li></ul>
  <ol><li>Ordered list inside ol ol</li></ol>
</ol>

<ul>
  <li>Unordered list</li>
  <ol><li>Ordered list inside ul</li></ol>
</ul>

<ol>
  <li>Ordered list 1</li>
  <ol><li>Ordered list inside ol ol</li></ol>
</ol>
</div>

I need somehow replace LI tags only inside div id="list" -> OL tags I need so that it replaces only LI tags only within the first OL tags and not UL or the once inside OL -> OL tags

I tried using preg_replace_callback but it only replaces all LI tags inside id="list" and from what i 开发者_如何学运维figured it will be over my head to limit replacement only with first ol tags and not the rest, so I been suggested to try out PHP DOM since it should be as easy as div id="list" -> OL

I would appreciate if someone got me started with the code, maybe with something as replacing all LI tags with in the first OL tag within the whole content.

You shouldn't do this with regex. It's a very bad way to parse (HT|X)ML. Use a genuine parser instead. Here's an example using PHP's DOMDocument class and the related DOMXPath:

<?php

$doc = new DomDocument(); 
$doc->loadXML('your HTML');
$xpath = new DOMXPath($doc);  

// get li elements in the first ol in the div whose id is list
$nodes = $xpath->query('//div[@id="list"]/ol[1]/li');

// change li elements to <li class='list'><div class='inline'>#####</div></li>
foreach ($nodes as $node) {
    $node->setAttribute('class', 'list');
    $number = $node->firstChild;
    $div = $doc->createElement('div');
    $div->setAttribute('class', 'inline');
    $div->appendChild($number);
    $node->appendChild($div);
}

// get the new HTML
$html = $doc->saveHTML();

NB also that you'll need to fix your ol and ul closing tags, which are currently unclosed.